Proposed studies are aimed at determining the physiological processes in the small intestine that are associated with and responsible for immunity to Trichinella spiralis. The hypothesis to be tested is that the overall immune response is a biphasic phenomenon, an early response, which occurs within the first 24 hr after challenge infection, and a delayed response that occurs several days after challenge. It is hypothesized that the initial or "fast" response: (a) prevents the actual establishment of infective larvae, (b) does not involve inflammatory cell influx into the lamina propria, and (c) causes subtle pathophysiologic changes. In contrast, the delayed or "slow" response is: (a) directed at dislodging and expelling previously established worms, (b) characterized principally by acute mucosal inflammation, and (c) attended by many of the pathophysiologic changes associated with worm expulsion in a primary infection. Emphasis will be placed on characterizing and establishing the relative importance of the "fast" response. To test the proposed hypothesis experimentally, correlations will be made during challenge infections between worm burdens and an array of structural and physiological parameters in the small intestine. These correlations will be made beginning as early as 15 min following challenge. These studies will be carried out on a temporal basis until worms are completely expelled from the intestine and structural and physiological parameters return to normal. Specific roles of factors such as intestinal motility, intestinal secretion, prostaglandins and intestinal mucous production in acquired resistance will be examined. Parallel studies will also be carried out in immunized animals maintained by total parenteral nutrition (TPN) to determine what intestinal factors, or lack thereof, can explain why immunized animals maintained for two weeks without oral food intake are unable to reject infective larvae as effectively as immunized, orally fed hosts. The ultimate goal behind these studies is to provide information for the development of immunological methods to prevent or control parasitic diseases.